Can't change `scroll` type legend to `plain` type legend

### Version
4.2.1

### Reproduction link
[https://gallery.echartsjs.com/editor.html?c=xp9j1rfiOF&v=1](https://gallery.echartsjs.com/editor.html?c=xp9j1rfiOF&v=1)

### Steps to reproduce
见链接

### What is expected?
分页图例切回普通图例时生效

### What is actually happening?
分页图例切回普通图例时不生效